1. Field of the Invention
The present invention generally relates to an image forming apparatus such a copying machine, printing machine or facsimile machine, and more particularly to an image forming apparatus having reduced noise.
2. Description of the Related Art
It is generally known to provide an image forming apparatus such a copying machine with a mass storage device, e.g., a hard disk device or a magneto-optic disk device having a driving means such a motor for memorizing and/or reading digital signals. The driving means in such an apparatus operates continuously so as to avoid the need to reboot, even though the apparatus is out of operation. However, the driving speed of the motor for the mass storage device must be high in order to achieve an adequate data reading speed, resulting in a loud noise which is objectionable to users.
In addition, it is generally known that at least two kinds of sensors can be used in the image forming apparatus. One, generally called a photo sensor, is generally present in a sheet feeding section to detect the presence of a sheet by use of light reflected from the sheet, or in a reading section to detect the size of the original by use of light reflected from the original.
The other, generally called a digital sensor, as shown in FIG. 1, includes a clock pulse oscillator 31 such a crystal oscillator, a vibrator 32 and sensing film 33, and is generally present in a developing device, toner hopper or waste toner container in order to detect the toner quantity or toner density therein. The clock pulse oscillator 31 issues a clock pulse at several tens of kHz, which vibrates the vibrator 32 and the film 33. As the oscillation frequency of the film 33 changes with a change in the amount of toner facing the film, the sensor is able to detect the amount of toner in the device. But the vibrator 32 resonates the sensor base at a frequency of about 6 kHz, which causes the sensor casing to resonate at about 1 to 2 kHz and produce a 35 dB noise.
Noise of this level occurring intermittently and for a long time hinders users from doing their work. However, the conventional image forming apparatus does not take measures against such noise, so that being around the image forming apparatus becomes unpleasant.